The present invention relates to a process for producing alkoxysilanes and more particularly, to a process for producing alkoxysilanes which can provide alkoxysilanes having at least one Si--H bond in the molecule thereof in a high yield.
As a process for producing alkoxysilanes having an Si-H bond in the molecule thereof, there is hitherto known a process which comprises chlorosilanes having the Si--H bond with alcohols. According to this process, the reaction proceeds as shown by the following reaction scheme: EQU (CH.sub.3).sub.a H.sub.b SiCl.sub.4-a-b +(4-a-b) ROH.fwdarw.(CH.sub.3).sub.a H.sub.b Si(OR).sub.4-a-b +(4-a-b) HC1
Namely, as is clear from the reaction scheme described above, hydrogen chloride is by-produced together with the alkoxysilane having Si-H bonds but the by-produced hydrogen chloride is intermingled with the produced alkoxysilane. It is not only difficult to remove this hydrogen chloride but also the Si--H bond portion of the alkoxysilane is alkoxylated due to its presence. As a result, yield of the alkoxysilane having the Si-H bond is reduced. Giving an example, in the case of producing methyldimethoxysilane from methyldichlorosilane and methanol, the produced methyldimethoxysilane is methoxylated into methyltrimethoxysilane by the presence of the hydrogen chloride by-produced. As the result, yield of the objective methyldimethoxysilane is reduced.
In order to prevent such a reduction in yield of the alkoxysilane, there is known a method for preventing alkoxylation of the Si-H bond which comprises previously incorporating amines such as pyridine, etc. into the reaction system thereby to neutralize the by-produced hydrogen chloride.
In such a method, however, a step of filtering and separating the formed amine hydrochloride fine powders is required. Further a step of recovering the amine from the separated amine hydrochloride becomes complicated. Furthermore, the method described above involves problems that a part of the alkoxysilane produced is absorbed into the amine hydrochloride and the system must be subjected to a treatment for washing with large quantities of solvents in order to recover the alkoxysilane, and the like. Such problems are disadvantageous from an industrial viewpoint. Further, for similar purposes, in a process for producing the alkoxysilane using ethylenediamine or sodium methoxide, the Si--H bond in the alkoxysilane is alkoxylated so that the process is not practical.
Further as a method other than those described above for producing the allkoxysilane by the reaction of chlorosilanes and alcohols, there is provided, for example, a method which comprises introducing alcohols into liquid chlorosilanes without contacting the alcohols with chlorosilanes presented in the gaseous phase, stepwise proceeding alkoxylation of the chlorosilanes and performing the final esterification step with heating (Published Unexamined Japanese Patent Application No. 95518/1979).
As is evident from examples of the published application supra, however, such a method cannot provide the objective alkoxysilane having an Si--H bond in high yield unless a reaction apparatus equipped with a reflux condenser cooled to -48.degree. to -82.degree. C. is necessarily used. That is, such a technique contemplates to increase the yield, by performing the final esterification with heating thereby to increase a rate of generating hydrogen chloride and a rate of removing hydrogen chloride and as the result, to shorten the contact time of the formed alkoxysilane having an Si--H bond with hydrogen chloride and deeply cool the condenser, thus preventing the loss of the unreacted chlorosilane and the formed alkoxysilane by being accompanied with hydrogen chloride. However, it is necessary to deeply cool the condenser, as described above so that energy consumption is very large and such is industrially disadvantageous.